Potamogeton capillaceus J. L. M. Poiret

Rhizomes present; cauline stems compressed, without dark spots, 10–35 cm long. Turions absent. Nodal glands absent. Leaves submersed and floating, although either type may be absent on certain individuals, alternate, more or less spiraling. Submersed leaves sessile; ligules inconspicuous, adnate to blade, reddish brown, not fibrous, not shredding apically, persistent to deliquescent, convolute, 1.5–2.3 cm long, adnate ca. 1/2 of length, the apex obtuse; leaf blade lax, light green to reddish brown, linear, often arcuate, 1–1.3 cm long, ca. 0.1 mm wide, with 1 veins, 1–2 rows of lacunae each side of midrib, the base auriculate, not clasping, without basal lobes, the margins entire, the apex acute, without a bristle tip, not cucullate. Floating leaves petiolate; petiole continuous in color to apex, compressed, 0.7–0.8 cm long; leaf blade adaxially light green, elliptic to obovate, 0.8–1.6 cm long, 3–8.5 mm wide, the veins 3–7, the base cuneate, the apex acute to obtuse, without terminal bristle. Inflorescences unbranched, both proximal submersed and distal emersed; proximal peduncles clavate, recurved, 0.3–0.5 cm long; proximal spikes capitate, 2–3 mm long; distal peduncles clavate, turgid, axillary or terminal, erect to slightly recurved, 0.6–1.5 cm long; distal spikes emersed, cylindrical, 0.3–2.8 mm long, the nodes 8–16, the internodes 0.2–0.7 mm long. Flowers alternate; perianth spathulate to ovate, clawed, the claw 0.1–0.3 mm long, the blade 0.5–0.9 mm long, 0.5–0.7 mm wide; anthers 0.2–0.3 mm long; carpels 4. Fruiting gynophore absent. Fruits circular, greenish brown, compressed, abaxially angled, laterally angled, 1–1.5 mm long, 0.9–2 mm wide; abaxial angles winged; lateral angles winged, with sharp points; beak erect, ca. 0.1 mm long; tubercules absent; embryo more than one full spiral.

Flowering and fruiting spring--fall. Ponds, lakes, streams, and rivers; 5--2500 m; Ala., Ariz., Ark., Calif., Colo., Conn., Fla., Ga., Idaho, Ind., Ill., Iowa, Kans., Ky., La., Md., Mass., Minn., Miss., Mo., Mont., Neb., Nev., N.J., N.Y., N.C., Ohio, Okla., Oreg., Pa., S.C., S.Dak., Tenn., Tex., Va., W.Va., Wis., Wyo.; Mexico.

This is very likely the most common species of Potamogeton in the southeastern United States. Fernald (1932) separated this species into two species, P. diversifolius s.s. and P. capillaceus and Correll and Johnston (1970) divided the species into two varieties, var. diversifolius and var. trichophyllous T. Morong. Potamogeton diversifolius var. trichophyllous actually is misapplied, as the name really refers to the more northern Potamogeton bicupulatus M. L. Fernald. We are, however, following Klekowski and Beal (1965) in accepting only one taxon, as we have studied the species over much of its range and reached similar conclusions to those of Klekowski and Beal.

Selected References: Correll, D. O. and M. C. Johnston. 1970. Manual of the vascular plants of Texas. Texas Research Foundation. Renner, Texas. 1881 pp. Klekowski, E. J. and E. O. Beal. A study of variation in the Potamogeton capillaceus--diversifolius complex (Potamogtonaceae). Brittonia 17: 175--181.